Hydraulic recoil spring?

[barnbwt]

"^Ohh, that's good. I see. So higher pressure may make the case take longer to retract because of higher "adhesion" to the chamber wall. I didn't think of that."
It's not really a duration thing so much as a deformation thing. The high pressure on the interior "peens" the brass outward (the brass actually liquefies under pressure). Obviously, the brass does not change in volume, so the enormous surface pressure does not actually move the brass/chamber walls outward significantly, but the end result is the brass is larger than the chamber once removed. That's why re-chambering fired brass in high pressure cartridges is usually somewhat difficult; the brass is bulged outward slightly due to compression on the interior of the case walls caused by the high chamber pressures.

You end up with brass that's under compression on the inside, and under tension on the outside.

I would imagine the far bigger difference in FNX vs Glock performance would be the exact differences between the chambers (feed ramp geometry/etc. could probably effect how snug the round was wedged in there)

Another interesting question would be whether the barrel truly drops straight down or not; if it moves backward or even pivots on corner relative to the breech face as it cams down, it has to compress the chambered case a little. In a high-pressure cartridge where the expanded case causes residual tension after the pressure has dropped both radially and against the breechface, the slight forward motion of the breechface might result in a bind that saps the action of needed energy.

TCB

 

[GLOOB]

For some reason I woke up thinking about Tuner's rope analogy. And I think I figured out how someone can misperceive it.

Take a 1911 slide and load a cork on a string into the chamber. Take the slide in one hand, and take the string in the other. Pull on the string.

As the cork slides through the barrel, your arms move apart. One or the other, it's hard to say which moves more. It's probably about equal. (That doesn't matter anyway, because your arms are adding mass to the system, and you're standing on the ground, and you are bringing the earth into the system, and, well, let's forget that). Bottom line is nothing really interesting happens, yet.

But when the cork pops out, your arms would fly apart, and the slide would finally (air quotes) start to move back. And this is why Tuner insisted on psi or air pressure making the slide move back. Once the cock pops, now (it would appear that) the air pressure equates to the equal and opposite force of your two arms, and that this is what is making the slide go back!

And in fact, he is right! And if you replace your arms with, say, two infinitely long massless springs of the same strength, on either end, the slide and cork would now (actually, still) be moving apart at velocities (and still accelerating) in the correct ratios.

Of course the acceleration curve looks totally different in a firearm. But that's totally fine with me, because it's still a valid model for looking at... well what, specifically? And there's the problem.

The problem is not with the model. It's that you are looking only at what happens after the bullet leaves the barrel. What about before the cork pops? We can see this, if we take the experiment further. When you you replace your arms with these massless springs (a mental picture of pure force, force forward equal to force backward), the first part of the experiment would look exactly the same as what happens after the cork pops, only in slower motion. The relative rate of movement between cork and slide would be the same, and that is cork moving faster, slide moving slower, in a ratio determined by their respective masses. If you take high speed video of this experiment, you could find a sequence of frames in there that would look quite a lot like a gun firing from the very beginning to end, no matter the actual differences in acceleration curves. Well, if you made the cork weigh 230 gr, first.

 

[JRH6856]

The problem is this model only looks at what happens after the bullet leaves the barrel. It totally ignores what is going on before the cork pops. And that is what I thought we were all interested in.

But we weren't all interested in the same thing. I was interested in the difference between when the bullet was in the barrel and after it left. And I think Tuner was as well. Everyone else just stopped talking once the bullet left the barrel like nothing else was happening.

And that is why I said it was like 6 blind men and the elephant.

 

[GLOOB]

And that is why I said it was like 6 blind men and the elephant.

Well, not exactly. Most of us were looking at the trunk and saying, this is definitely a trunk, and it proves that this is a trunk. At least one or more of us had on occasion said, look at this tail. It proves we're looking at a unicorn, so you're holding a horn, not a trunk.

I would imagine the far bigger difference in FNX vs Glock performance would be the exact differences between the chambers (feed ramp geometry/etc. could probably effect how snug the round was wedged in there)

I can see where you are coming from there, but I do not necessarily agree, in this case. After shooting these over loads in my Glock, the Glock continued to malfunction with the stock spring and regular loads, just not as bad. At that time I was still shooting factory ammo, too. In this case 180 gr PMC, which was also pretty hot (really stung the hands). I determined the recoil spring was shot. It was significantly weaker than the stock replacement I ordered and which eliminated the problem. Also, Glock chambers are slicker than owl snot, and this one is no different. There are no chatter marks or machine marks of any kind in a mandrel forged barrel, cuz there is no cutting. Or maybe that slickness makes it stick worse under high pressuure? Lol. I don't really know.

The other reason I remain stubborn is that my FNX appears to be a total stud in terms of duration of breechlock. The barrel doesn't even start to drop until somewhere between 0.15" and 0.19". I am being generous with my measurement range, because it's hard to measure on this gun. But it could be twice the distance as on my Glock, which is exactly 0.09" plus or minus only a few mics. The FNX slide weighs more, and it has a hammer spring to contend with, too (whereas the Glock's striker spring compresses on the return trip). If the Glock has a stronger recoil spring, it's not by much in comparison. I know that second tenth of an inch happens a lot, lot faster, but it is really not a difference between 0.09 and 0.19... it's the difference between where the bullet leaves the muzzle. If you subtracted 0.08" from both (just as a complete shot in the dark as to when the bullet might exit) then you're looking at the difference between 0.01" and as high as 0.11" of slide travel during which the brass can retract. After the bullet is gone, the slide doesn't get all that much faster, presumably (it might from the rocketing gases escaping). But if held constant, the FNX could have on the order of 10 times as long between where the bullet exits and the slide starts to unlock, very roughly. And I know this still doesn't prove the chamber isn't a bigger factor, but I am not ready to accept that explanation, yet. And I know I should be looking at where the barrel and slide start to separate, not where they start to unlock. But I didn't measure that information, yet. IIRC, though, the FNX unlocks a lot slower, over a longer distance, in which case it would remain quite impressive - the absolute difference in distance would be even greater, though the relative difference would not be as impressive as the 10 fold projection when measured from that point of barrel egress and separation, rather than between egress and campoint. Even if the difference only ends up being 50-100%, that might be pretty significant. I think it could be even more. Maybe I'll dig out the calipers to figure this out at some point.

Another interesting question would be whether the barrel truly drops straight down or not; if it moves backward or even pivots on corner relative to the breech face as it cams down, it has to compress the chambered case a little. In a high-pressure cartridge where the expanded case causes residual tension after the pressure has dropped both radially and against the breechface, the slight forward motion of the breechface might result in a bind that saps the action of needed energy.

I'm going to go ahead and agree. As the barrel cams down, the casehead must slide across the breechface against which it has just been crushed. But the muzzle end of the barrel has a fixed pivot. So aside from the friction, the top edge of the casehead may have to be smushed a little in the process as the barrel rotates. This really depends on exactly how the locking lugs fit, though. It doesn't have to happen, but it could. I mean it should have to happen if the lugs are cut exactly perpendicular on the opposing faces. But the lugs are relatively short, so this shouldn't be too big of an effect, even if it does continue to happen on a worn-in barrel and slide. But I figure the edges of the locking lugs would slightly round off, approximating the requisite arc.

If you mark a bunch of cartridges on the casehead and hand chamber them to your registration mark, you might be able to measure a difference in the brass after it ejects?

*Edit: So I pulled out the calipers and the guns. I set the calipers up with two sets of wood clamps, so the depth stop is pointing up a half inch from the edge of my bench. I set the guns over the depthstop with the barrel on the bench, depth stop on a repeatable part of the front of the frame. Both at rest, and with the barrel fully retracted. Best I can get follows:

Glock: 245 mics
FNX: 346 mics

So using my original guestimequation, the FNX would have very roughly 61% more time between bullet egress and where extraction starts. Probably a bit longer, if you factor in everything else, subtracting for the longer barrel and potentially greater muzzle velocity (except glock barrels are usually faster for their length) and adding for the increased slide mass, and all the other whatnots. The difference in time between peak pressure and extraction would be on a similar order, since things happen very fast after that point and max velocity does not much change between those two barrels.

If I wanted to play with 200 gr bullets and/or higher pressures, I would do it in the FNX.